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A  CONNECTION  BY  PRECISE  LEVELING  BETWEEN 
THE  ATLANTIC  AND  PACIFIO  OCEANS 


BY 


DR.  JOHN    F.  jHAYFORD 


[Reprinted  from  Science,  JV^  S.  ,  Vol.  XXL ,  No.  5S9, 
Pages  673-674,  April  28,  1905.'] 


n  ^^^^ 


lEeprinted  from  Science,  N.  /S'.,  Vol.  XXI.,  No. 
539,  Pages  673-674,  April  S8,  1905. ] 


A    CONNECTION    BY    PRECISE    LEVELING    BETWEEN 
THE    ATLANTIC    AND    PACIFIC    OCEANS. 

On  October  4,  1904,  a  Coast  and  Geodetic 
Survey  party,  running  eastward  from  Seattle, 
Wash.,  met  a  similar  party,  running  westward, 
at  Hunts  Junction,  in  the  southeastern  part 
of  Washington.  The  party  running  from  east 
to  west  had  started  in  the  beginning  of  the 
season  from  a  bench  mark  of  which  the  eleva- 
tion had  been  fixed  by  a  long  line  run  during 
several  seasons  and  extending  westward  from 
the  precise  level  net,  composed  of  many  cir- 
cuits, which  covers  the  eastern  half  of  the 
United  States.  As  far  west  as  Norfolk,  Nebr., 
the  elevations  in  this  net  had  been  checked 
by  completed  circuits  of  precise  leveling  of 
the  highest  grade  of  accuracy.  The  joining 
of  the  two  lines  at  Hunts  Junction  completed 
the  first  connection  by  precise  leveling  be- 
tween the  Atlantic  and  the  Pacific. 

The  discrepancy  developed  at  the  junction 
was  .615  ft.  (=187.5  millimeters),  the  Pacific 
being  apparently  higher  than  the  Gulf  of 
Mexico  and  Atlantic. 

The  old  question  at  once  arises:  is  the 
Pacific  at  a  different  elevation  from  the  At- 
lantic? The  discrepancy  of  .615  ft.  must  be 
due  either  to  errors  in  the  tidal  observations 
which  furnished  the  connection  with  mean 
sea  level,  or  errors  in  the  leveling,  or  to  a  real 
difference  in  the  elevation  of  the  mean  sea 
surface  at  the  points  at  which  the  tidal  ob- 
servations were  made. 

The  three  principal  connections  with  sea 
level  concerned  are  at  Sandy  Hook,  near  New 
York  City,  at  Biloxi,  Miss.,   and  at   Seattle, 


Wash.  Six  years  of  tidal  observations  were 
taken  at  Sandy  Hook  and  five  years  at  each 
of  the  other  points.  The  range  in  the  six 
annual  means  at  Sandy  Hook  was  .322  ft., 
and  of  the  five  annual  means  at  the  stations 
at  Biloxi  and  Seattle  was,  respectively,  .100 
and  .204  ft.  These  ranges  are  not  sufficient 
to  account  for  the  discrepancy  of  .615  ft. 

The  shortest  line  of  leveling  of  the  highest 
grade  of  accuracy  from  Seattle  to  Sandy  Hook 
is  4,600  miles  (7,400  kilometers) ;  to  Biloxi, 
3,500  miles  (5,700  kilometers)  ;  and  to  Norfolk, 
the  point  at  which  the  line  to  the  westward 
leaves  the  thoroughly  checked  portion  of  the 
precise  level  net,  is  2,000  miles  (3,300  kilo- 
meters). 

If  it  is  assumed  that  the  discrepancy  (.615 
ft.)  is  simply  an  accumulated  error  in  leveling 
and  that  the  rate  of  accumulation  is  uniform 
between  Seattle  and  Biloxi,  it  is  at  the  rate 
of  one  foot  in  5,700  miles  (.033  millimeters 
per  kilometer).  Even  if  it  is  assumed  that 
the  accumulation  all  occurred  between  Seattle 
and  Norfolk,  it  is  at  the  rate  of  one  foot  in 
3,300  miles  (.057  millimeters  per  kilometer). 
This  is  an  extremely  small  error  of  leveling. 

Another  test  to  determine  whether  the  dis- 
crepancy is  a  possible  error  of  the  leveling 
may  be  applied.  The  probable  error  of  the 
elevations  at  Seattle,  as  carried  westward  from 
the  Gulf  and  Atlantic,  tiie  computation  being 
based  upon  the  discrepancy  developed  in  the 
circuits  in  the  eastern  part  of  the  United 
States,  was  db  76  millimeters.  The  actual  dis- 
crepancy is  two  and  one  half  times  this.  Ac- 
cording to  the  doctrine  of  chances,  such  a 
discrepancy,  two  and  one  half  times  the  prob- 
able error,  should  occur  about  once  in  ten 
times. 

Therefore,  it  is  not  safe  to  make  the  state- 
ment that  the  Pacific  is  higher  than  the  Gulf 
and  Atlantic;  the  extremely  small  discrepancy 
being  well  within  the  possible  limits  of  error 
of  the  precise  leveling  alone,  even  though  it 


be  assumed  that  the  leveling  in  question  is  of 
as  high  a  grade  of  accuracy  as  any  yet  done 
anywhere  in  the  world. 

One  is  apt  to  associate  observations  of  such 
extreme  accuracy  as  this  precise  leveling  with 
slow  progress  and  high  cost.  It  is  interesting, 
therefore,  to  note  that  three  thousand  miles 
out  of  the  thirty-five  hundred  between  Seattle 
and  Biloxi  have  been  leveled  since  the  begin- 
ning of  the  field  season  of  1899,  and  that  the 
average  rate  of  progress,  during  the  period 
1900-1904  (a  total  of  3,900  miles),  with  the 
new  type  of  precise  level  now  in  use  in  the 
Coast  and  Geodetic  Survey,  was  64  miles  of 
completed  line  per  month,  for  each  observer, 
and  that  the  average  cost,  per  completed  mile, 
was  $10,  including  salaries,  transportation 
and  bench  marks.  Each  completed  mile  was 
leveled  over  at  least  twice,  and,  in  some  cases, 
four  or  more  times.  This  rate  of  progress  is 
comparable  with  that  ordinarily  secured  in 
wye  leveling,  which  is  of  a  much  lower  order 
of  accuracy.  John  F.  Hayfobd. 


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PAflNPHLET  BINDEt 

Syracuse, 
Stockton, 


